An articulated system, such as the variable-setting diffuser blades of a gas turbine engine compressor, comprises parts moving with respect to each other. FIG. 1 shows schematically a variable-setting diffuser blade 1 mounted rotatably in the engine casing 3. The blade comprises a vane 12, a platform 13 and a root forming a pivot 14. The pivot 14 is housed in a radial bore or aperture formed in the casing 3, using sleeves 4 and 5 which are in sliding contact with the root forming the pivot 14. A washer 15 retains the blade in its housing. A lever 16, itself actuated by members which are not shown, causes the blade to rotate about the axis XX of the root to bring it into the required position with respect to the flow of air passing over the vane. The relative movements result from the sliding of the surfaces in contact which form a plain bearing, in this case the root and the sleeves. When the engine is running, it is found that the stresses to which the parts are subjected expose the contact surfaces to a degree of wear which can lead to losses of functionality of the system. The rate at which the contact surfaces become degraded depends on numerous parameters, the principal ones of which are related to the operating temperature, the contact pressure, the amplitude of the relative movements, and the environment.
In the case of a variable setting mechanism for gas turbine blades, a particular constraint is the requirement of operation in a non-lubricated environment. Only dry lubrication can be envisaged in this case to improve the contact conditions.
The materials used for diffuser blades are titanium alloys, steels, or nickel alloys. The casing material is generally a steel or a titanium alloy. The materials used for the sleeves are generally chosen from two groups, namely organic materials and inorganic materials. It is preferable to use organic materials if the temperature conditions permit, in other words at temperatures below 300-400° C., while inorganic bases are preferred at higher temperatures. All the wear prevention systems known at present have a limited life.
There is a need to provide new solutions which would increase the operating life of variable-setting diffuser mechanisms, and more generally the life of sets or pairs of parts which are in sliding contact with each other in the form of a plain bearing, during the operation of a machine.
The applicant's aim is to provide parts having surfaces forming plain bearing elements in which the wear is reduced, and in particular to propose new pairs of wear-resistant materials.
In particular, the applicant's aim is to resolve the problem of wear in the contact between the diffuser root and the sleeve, and to significantly increase the life of the variable-setting devices by proposing an inexpensive solution.